1. Field of the Invention
The present invention relates to an image forming system which performs image forming processing on fed sheets of printing paper and outputting of the imaged sheets.
2. Description of the Related Art
In recent years, a field called “on-demand printing” has attracted attention as a field relating to digital copying machines and printing. On-demand printing can meet a multi-type small-lot demand, and can be used to easily change the printing content. Accordingly, on-demand printing is suitable for use in producing documents, such as manuals, and brochures for individual users. In addition, on-demand printing IS advantageous in that it reduces the number of printed sheets that need to be kept in stock and reduces steps and time during in-line processing from data input to completion of bookbinding. In addition, on-demand printing has a feature in that data transfer is facilitated by using a digital line to establish connection to a client. Therefore, the time to delivery can be considerably reduced and the delivery cost can be reduced.
Technologies relating to on-demand printing include use of an image recording apparatus such as a digital copying machine. With the improvement in image quality in the recent years, the image quality of copies produced by copying machines has reached a level close to the image quality of prints.
PCT Japanese Translation Patent Publication No. 2001-506212 discloses an image forming system using a copying machine meeting on-demand printing needs. In this image forming system, in order to cope with a variety of materials, a plurality of printing paper decks that can store large numbers of sheets of printing paper are connected to one another.
In addition, Japanese Patent Laid-Open No. 2000-211803 discloses an image forming system that uses consecutive job operations to perform post-processing on imaged sheets output from a copying machine. Typical post processing includes an inserting process in which a sheet such as a cover sheet or a divider is inserted between sheets output from a copying machine performing Z-folding (e.g., a process that performs Z-folding of a A3 size sheet into a A4 size), a stapling process for binding a bundle of sheets, a punching process for punching sheets, and a binding process such as gluing and bookbinding.
FIG. 25 shows an example of the above image forming system. In this image forming system, a copying machine A is connected to a plurality of large-capacity printing paper decks B connected to one another, so that a large number of sheets of printing paper of various types can be fed to the copying machine A. In addition, the copying machine A is connected to a sheet ejecting unit C in which post-processing, such as a Z-folding process, an inserting process, a stapling process, a punching process, and a bookbinding process, is performed on imaged sheets of printing paper produced by the copying machine A.
In addition, Japanese Patent Laid-Open No. 5-53478 discloses an image forming apparatus having a copying machine and a paper feeding unit that can accommodate sheets of paper of plural types. This image forming apparatus includes a re-feeding unit which stacks sheets fed by the feeding unit and which feeds the stacked sheets to a printer.
In the image forming system shown in FIG. 25 in which the large-capacity printing paper decks B are connected, it is common for a carriage path from each printing paper deck B to the copying machine A is to be shared. This structure has the following problems.
For example, in the case of a job that makes a bundle of sheets of material paper of plural types, a change in paper type may require a change of the printing paper deck B in use. For example, when paper feeding from one printing paper deck B which is the closest to the copying machine A is changed to another printing paper deck B which is the farthest from the copying machine A, paper feeding from the printing paper deck B under normal feeding timing increases an interval (hereinafter referred to as a “sheet interval”) between sheets of printing paper. This causes a problem in that productivity decreases.
Productivity cannot be maintained, with the sheet interval maintained to be constant, unless techniques for solving the above problems are performed. Techniques include changing the paper feeding timing or the like in view of the number of the printing paper decks B or the arrangement of the printing paper decks B for connection, carrying printing paper on the carriage path at an increased speed in order to reduce the sheet interval, or complex control of the carriage carries a sheet of printing paper to a predetermined position on the carriage path and allows the sheet to be on standby beforehand, and restarting the sheet carriage at the standby position.
In addition, the image forming apparatus disclosed in Japanese Patent Laid-Open No. 5-53478 includes a re-feeding unit which stacks sheets of printing paper from a plurality of paper feeding units and which supplies the sheets to a printer. However, during a period in which the sheets are carried from each paper feeding unit to the re-feeding unit, the printing paper is not fed to the printer, so that the productivity of the printer is low. Also, when sheets of printing paper of different types are stacked in the paper feeding units, for example, it is difficult to alternately feed the sheets of different types to the printer.